Voltage makes a differnece to top speed performance, but do you need it?
You mention 1.8-3 Nm, so you are within the Nema 23 range, so look for a motor that is as high current as possible, to keep the inductance as low as possible.
There are disadvantages to high voltage as well; the motor will get a lot hotter, and will make a lot more noise.
In my experience for a nema 23 motor 40-50 V is fine, and going up to 70 V will only give you a performance increase at the higher speeds. (Over 300 RPM)
Do you want to pay 50-60% more for 15-20% more performance?
What torque and speed do you need?
Nema 34 motors are different, and these really need high voltage to get the best from them.